Hello,

Recently I've booked ticket on United using the miles for flights that involve Thai Airways on 3 flights.
When I purchase regular ticket, not using my miles, in the United app I can see option Additional Information where I can see other airlines booking reference number. Last time I was able to use it to select my seats on ANA.
Now, I have tickets using miles and I don't see another reference number. Not surprisingly, I can only select seats on United operated flights.
How can I find out my reference number for my Thai flights?

Thank you